The invention relates to an apparatus for measuring moisture conditions, more particularly for measuring the quantity of precipitation such as rain or snow which has fallen to the earth and the subsequent rate of evaporation of that precipitation.
Precise knowledge of the amount of precipitation which falls to the ground at various places in a region is becoming increasingly important. Such knowledge permits accurate prediction of future crops and a rational scheduling of irrigation and other watershed management. In addition, such information is vital in managing water resources to avoid waste and flooding.
The rate of precipitation, typically the amount of rainfall which falls to the ground in a given time period, is now measured by conventional rain gauges utilizing tipping buckets. Water falls first into a small bucket which empties into a larger bucket when the smaller bucket holds a given quantity of liquid. The larger bucket in turn tips into a yet larger bucket when full. In this way the amount of rainfall can be ascertained and even transmitted to some remote location.
The disadvantages of such rain gauges are well known. First, the amount of liquid which causes tipping of a given bucket may vary from apparatus to apparatus, particularly as the device weathers and maybe even partially damaged by the elements. Second, the devices are mechanically complicated and apt to failure. Third, the mechanical complexity of the devices results in a cost which is too high to permit use of the number of devices desired for most applications.
The present invention relates to a simple rain gauge which also has the capability of measuring other moisture conditions and which contains no moving parts. Precipitation is received within an open container having therein an absorbant material which absorbs the rainfall and has a dielectric constant varying as a function of the volume of precipitation absorbed. Conductors extend in the media, preferably forming two pairs of separated grids. An ac signal is applied to the grids at least periodically to measure the impedance between the grids and thereby the dielectric constant of the media and the volume of precipitation absorbed. Measurement in this fashion is discussed further in the patent to Walsh U.S. Pat. No. 4,288,742 and in application Ser. Nos. 623,230 filed June 21, 1983 and U.S. Pat. No. 416,232 filed Sept. 7, 1982, the disclosures of which are hereby incorporated by reference.
A heater can also be disposed within the container for drying the absorbant material either periodically or when a rainstorm or snowstorm has stopped. A plurality of different media having different absortivity can be disposed either to receive precipitation simultaneously or from an absorbant media located above it to indicate the amount of precipition received in different time periods. The container may have an upper open portion above the absorbant medium with a heater disposed therein for melting snow to provide an accurate and continuous indication of the precipitation received in a snowstorm.
A sensor such as a pair of contacts disposed in a groove on the top of the container may be utilized to indicate when a rainstorm has ceased and a measurement of the amount of precipitation received during that rainstorm can be taken.